1. Field
The present disclosure generally relates to endoscopes, and more particularly to a rigid endoscope.
2. Prior Art
An endoscope of this type is known from DE 10 2004 009 219 A1. The objective lens is held by a spacer device at a distance from the window, by which means the precise optical calibration of the objective lens is assured.
In the known structure, the objective lens is supported against a stop on the fiber tube formed by a step protruding inward. Thus, a precise preservation of the distance of the objective lens with regard to the window fixed on the fiber tube is possible. However, disadvantages arise from this structure.
Due to the projection protruding inward, a diameter reduction of the fiber tube arises. This results in an increase of the tolerances during the assembly of the window. This window must be held during the fixing of the fiber tube, which e.g. usually takes place by soldering. For this purpose, in general a mandrel is used which is pushed forward from the inside through the fiber tube up to the window, which mandrel supports the window on a plurality of points or in a planar way and holds it during the soldering. The projection forming the stop reduces the inner diameter of the fiber tube at this point so that the diameter of the mandrel that is able to be fed through must be reduced. The support surface of the mandrel is thus reduced at the window and by this means the calibration precision. This can lead to interfering tiltings of the window.
A further disadvantage of the step forming the stop is an impaired cleanability in this area. In this case, e.g. soldering flux residue remaining in the corner, could offgas in the later hermetically closed fiber tube and blur the optical surfaces of the objective lens due to fogging.
In the region between the window and the objective lens, an additionally previously unsolved problem persists, which results from the fixing of the window. The window is soldered in the usual way on its peripheral edge to the inner surface of the fiber tube. For this purpose, a preparation of the surfaces to be soldered is necessary. The glass of the window must be metallized on the edge, but also an inner gold plating of the fiber tube is advantageous in order to guarantee a truly secure fixing. Thereby, it is in turn commendable for a number of mostly manufacturing-caused reasons, to allow this gold plating to project over the region to be soldered in the proximal direction. Also, the metal solder used for soldering is allowed to swell out of the solder gap in the proximal direction for a number of reasons.
After completing the soldering of the window, highly reflecting surface regions thus result from the gold plating and/or the soldering on the inner side of the fiber tube in the region between the window and the objective lens, which result in interfering reflections which can radiate from the sides into the beam path and to the eye of the observer.